Former government drugs adviser Prof David Nutt has said that regulations should be relaxed to enable researchers to experiment on mind-altering drugs.
Prof Nutt told BBC News that magic mushrooms, LSD, ecstasy, cannabis and mephedrone all have potential therapeutic applications.
However, he said they were not being studied because of the restrictions placed on researching illegal drugs.
He said the regulations were "overwhelming".
His comments followed the publication of new research by his group in the Proceedings of the National Academy of Sciences, which suggests that the active ingredient in magic mushrooms could be used to treat depression.
"I feel quite passionately that these drugs are profound drugs; they change the brain in a way that no other drugs do. And I find it bizarre that no-one has studied them before and they haven't because it's hard and illegal," he said.
A Home Office spokesperson said: "The Home Office licensing regime already enables research to take place through a system of controlled drug possession licences, allowing bona fide institutions to carry out scientific research.
"This regime recognises the importance of such research and enables that to take place in an appropriate environment, ensuring the necessary safeguards are in place."
Prof Nutt was sacked by the home secretary from his government advisory role three years ago for saying that ecstasy and LSD were less harmful than alcohol.
He says his new research indicated that there were no "untoward effects" from taking magic mushrooms and that it should not be illegal to possess them.
Prof Nutt and his team scanned the brains of volunteers who had been injected with a moderate dose of psilocybin, the active ingredient of magic mushrooms.
They had expected higher activity in areas of the brain associated with visual imagery. But in fact they found that the drug switched off a network of interconnected regions of the brain which regulated an individual's sense of being and integration with their environment.
The researchers say that this alters consciousness because individuals are less in touch with their sensations and normal way of thinking.
They also found that psilocybin also turns off a part of the brain which is overactive in some forms of depression. So Prof Nutt believes that the drug could be used as an antidepressant and has applied to the Medical Research Council to carry out a small patient study to see if this is the case.
"There's some research from the US which shows that when used in a psycho-therapeutic context it can produce quite long-lasting changes to a person's sense of well-being - changes that can last for years," he says.
He also said that there was nothing in the brain scans or follow-up studies which would suggest that if taken in moderate quantities the drug was unsafe.
"People who use them regularly seem to do that. They seem to use them on an annual basis in order to enjoy the experience but also because it has this positive reaffirming effect.
"And there are certainly examples of people who take magic mushroom tea for obsessive compulsive disorder to keep it under control.
"So it may be that there are broad utilities of these kind of compounds in terms of mental well-being. I don't know - I think it's very much a question to be answered."
A second study, due to be published online by the British Journal of Psychiatry on Thursday, found that psilocybin enhanced volunteers' recollections of personal memories, which the researchers suggest could make it useful as an adjunct to psychotherapy.
However, Martin Barnes, chief executive of DrugScope, said: "The research published today does not directly address whether or not magic mushrooms are harmful.
"Instead, it looks at how psilocybin, the active chemical in magic mushrooms, affects the brain."
Prof Nutt also said that he believed that possession of magic mushrooms should not be illegal, adding that its status as a controlled drug was hampering research.
"Research has been minimal, if not non-existent, on psychedelic drugs because the regulations are so overwhelming," he said.
"I would say that this is the most obvious unexplored area of neuroscience; drugs which change the brain in a fundamental way and yet we don't bother studying them because it's too difficult or we are to scared of falling foul of the regulators or the media."
But Mr Barnes from DrugScope cautioned that the recreational or problematic use of drugs should not be conflated with the important issue of researching possible therapeutic or medical benefits that some psychoactive substances may offer.
"A carefully controlled and supervised study, using a pure formulation of psilocybin under controlled conditions, is very different from how most people would ingest the substance in magic mushrooms.
"As with medicines which use active chemicals present in cannabis, pharmaceutical products derived from any psychoactive substances will differ significantly from street drugs."
Prof Nutt resists comparisons with the 1960s guru Timothy Leary who advocated the use of LSD. His view was that if everyone took LSD all the time they would be better people. They would have nicer, happier lives.
"I'm not recommending anyone taking any drugs. I'm just suggesting we need to have a more scientific rational approach to drugs and vilifying drugs like psilocybin whilst at the same time actively promoting much more dangerous drugs like alcohol is totally stupid scientifically."
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